AP Biology Unit 3 Study Guide

Topics Covered

• Cellular Energetics

  • Understanding metabolism: anabolism and catabolism

  • ATP as energy currency

  • Enzyme structure and function

  • Factors affecting enzyme activity (pH, temperature, concentration)

• Photosynthesis

  • Overview of photosynthesis process

  • Light-dependent reactions and Calvin cycle

  • Chloroplast structure and function

  • The role of pigments in photosynthesis

• Cellular Respiration

  • Overview of cellular respiration stages: glycolysis, Krebs cycle, electron transport chain

  • Differences between aerobic and anaerobic respiration

  • Energy yield of cellular respiration

• Interdependence of Photosynthesis and Cellular Respiration

  • How products of photosynthesis are used in cellular respiration

  • Importance of these processes for energy flow in ecosystems

• Cell Communication

  • Types of signaling (autocrine, paracrine, endocrine, etc.)

  • Signal transduction pathways

  • Importance of cell receptors

Key Terms

• Metabolism

• ATP (Adenosine Triphosphate)

• Enzyme

• Photosynthesis

• Cellular respiration

• Glycolysis

• Krebs cycle

• Electron transport chain

• Signal transduction

Important Diagrams to Study

• Structure of ATP

• Photosynthesis reaction equation

• Flow of energy in cellular respiration

• Various cell signaling pathways

Tips for Studying

• Make flashcards for key terms

• Practice diagrams for labeling

• Form study groups to discuss concepts

• Utilize quizzes to test understanding

• Refer to past AP exam questions for practice.

Here are definitions for some key terms related to cellular energetics:

1. Metabolism: The sum of all chemical reactions occurring within an organism, divided into anabolism (building up substances) and catabolism (breaking down substances).

2. ATP (Adenosine Triphosphate): The primary energy carrier in cells, used to power various cellular processes.

3. Enzyme: A biological catalyst that speeds up chemical reactions in cells without being consumed in the reaction.

4. Photosynthesis: The process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose.

5. Cellular Respiration: The metabolic process by which cells convert sugars into energy in the form of ATP, using oxygen (aerobic respiration) or without it (anaerobic respiration).

6. Glycolysis: The first stage of cellular respiration, occurring in the cytoplasm, where glucose is broken down into pyruvate, yielding a small amount of ATP.

7. Krebs Cycle: A series of chemical reactions in the mitochondria that further breaks down pyruvate to carbon dioxide, generating energy carriers for the electron transport chain.

8. Electron Transport Chain: A sequence of protein complexes in the inner mitochondrial membrane that uses electrons from NADH and FADH2 to generate ATP through oxidative phosphorylation.

9. Signal Transduction: The process by which a cell responds to signals or stimuli from the environment, involving the reception of a signal and the subsequent cascade of responses within the cell.

Light-Dependent Reactions: These are the first stage of photosynthesis that occurs in the thylakoid membranes of chloroplasts. They require light to occur and involve the absorption of light energy by chlorophyll and other pigments, which is then converted into chemical energy in the form of ATP and NADPH. Water molecules are split, releasing oxygen as a byproduct. The primary functions include the generation of ATP and NADPH, which are essential for the subsequent Calvin cycle (light-independent reactions).

Fermentation vs. Cellular Respiration:

• Fermentation (Alcoholic Fermentation):

  • An anaerobic process that occurs in the absence of oxygen.

  • Converts sugars, such as glucose, into cellular energy, producing ethanol and carbon dioxide as byproducts.

  • Commonly used by yeast in the production of alcoholic beverages and bread.

  • Yields a small amount of ATP (typically 2 ATP per glucose).

• Aerobic Respiration:

  • Requires oxygen to occur.

  • Involves glycolysis, followed by the Krebs cycle and the electron transport chain.

  • Converts sugars into carbon dioxide and water while generating a larger yield of ATP.

  • Total ATP yield can be around 30-32 ATP per molecule of glucose.

Key Differences:

• Oxygen Requirement: Fermentation is anaerobic, while respiration is aerobic.

• End Products: Fermentation produces ethanol and CO2, while aerobic respiration produces CO2 and water.

• Energy Yield: Fermentation yields less energy (ATP) compared to aerobic respiration.

There are two main types of fermentation:

1. Alcoholic Fermentation:

   • An anaerobic process that occurs in the absence of oxygen.

   • Converts sugars, such as glucose, into cellular energy, producing ethanol and carbon dioxide as byproducts.

   • Commonly used by yeast in the production of alcoholic beverages and bread.

   • Yields a small amount of ATP (typically 2 ATP per glucose).

2. Lactic Acid Fermentation:

   • An anaerobic process that occurs in muscle cells and some bacteria.

   • Converts glucose into cellular energy, producing lactic acid as a byproduct.

   • Occurs during strenuous exercise when oxygen levels are low, leading to the build-up of lactic acid in muscles, which can cause fatigue.

   • Also yields 2 ATP per glucose.

These two fermentation types play significant roles in various biological processes and applications, such as food production and energy metabolism.

Thermogenesis and Non-ThermogenesisThermogenesis:

• The process by which the body produces heat.

• Primarily occurs in brown adipose tissue (brown fat), where energy is utilized to generate heat rather than stored as fat.

• Essential for maintaining body temperature, particularly in cold environments.

• Can be activated through methods such as cold exposure and certain hormones like norepinephrine.

Non-Thermogenesis:

• Refers to energy expenditure that does not involve the production of heat.

• Includes processes such as basal metabolic rate (BMR), physical activity, and the thermic effect of food (TEF), which is the energy required for digestion, absorption, and metabolism of food.

• In this state, energy is used primarily for maintaining bodily functions and daily activities, without significant heat production.

Cellular Respiration Cycle with 38 ATP YieldCellular respiration involves several stages: glycolysis, Krebs cycle, and the electron transport chain. The overall reaction of cellular respiration can be represented as follows:

General Equation for Cellular Respiration:C6H12O6 (glucose) + 6 O2 → 6 CO2 + 6 H2O + (up to 38 ATP)

1. Glycolysis

• Location: Cytoplasm

• Reactants: Glucose (C6H12O6)

• Products: 2 Pyruvate, 2 ATP (net gain), 2 NADH

• ATP Yield: 2 ATP per glucose molecule

2. Krebs Cycle (Citric Acid Cycle)

• Location: Mitochondria

• Reactants: Acetyl-CoA (derived from pyruvate), NAD+, FAD, ADP, and inorganic phosphate

• Products: 2 CO2, 3 NADH, 1 FADH2, 1 ATP per acetyl-CoA (2 ATP per glucose since one glucose generates two acetyl-CoA molecules)

• ATP Yield: 2 ATP from Krebs Cycle (net gain)

3. Electron Transport Chain

• Location: Inner mitochondrial membrane

• Reactants: NADH, FADH2, O2

• Products: H2O; ATP (produced via oxidative phosphorylation – approximately 34 ATP)

• ATP Yield: About 34 ATP

Total ATP Yield

• Glycolysis: 2 ATP

• Krebs Cycle: 2 ATP

• Electron Transport Chain: ~34 ATP

• Total: Approximately 38 ATP per glucose molecule

Summary of Reactants and Products

• Total Reactants for Cellular Respiration:

  • Glucose, Oxygen

• Total Products for Cellular Respiration:

  • Carbon Dioxide, Water, ATP (up to 38 ATP)

This overall process illustrates how glucose is metabolized to produce ATP, vital for cellular energy.

Cellular respiration consists of four main steps:

1. Glycolysis

   • Location: Cytoplasm

   • Reactants: Glucose (C6H12O6)

   • Products: 2 Pyruvate, 2 ATP (net gain), 2 NADH

   • ATP Yield: 2 ATP per glucose molecule

2. Pyruvate Oxidation

   • Location: Mitochondria

   • Reactants: 2 Pyruvate

   • Products: 2 Acetyl-CoA, 2 CO2, 2 NADH

   • Pyruvate is converted into Acetyl-CoA before entering the Krebs Cycle.

3. Krebs Cycle (Citric Acid Cycle)

   • Location: Mitochondria

   • Reactants: Acetyl-CoA, NAD+, FAD, ADP, inorganic phosphate

   • Products: 4 CO2, 6 NADH, 2 FADH2, 2 ATP (2 ATP per glucose molecule)

   • ATP Yield: 2 ATP from Krebs Cycle (net gain)

4. Electron Transport Chain and Oxidative Phosphorylation

   • Location: Inner mitochondrial membrane

   • Reactants: NADH, FADH2, O2

   • Products: H2O, ATP (produced via oxidative phosphorylation)

   • ATP Yield: Approximately 34 ATP

Total ATP Yield:
Glycolysis: 2 ATP
Pyruvate Oxidation: 0 ATP
Krebs Cycle: 2 ATP
Electron Transport Chain: ~34 ATP
Total: Approximately 38 ATP per glucose molecule.